Method of making a bearing assembly

ABSTRACT

A method of making a bearing assembly is disclosed in which a bearing support housing having a spherical bore therethrough is spray-coated entirely with a polymer primer coating and then coated with a polymer top coating, after which a bearing sub-assembly is placed within the spherical bore in the housing. During application of the top coating, an insert is placed within the spherical bore in the housing to prevent the bore from being coated with the top coating. The primer coating is sufficiently pliable to enable bearing sub-assemblies within a range of tolerances to be properly seated within the spherical bore.

This is a division of application Ser. No. 07/452,255, filed Dec. 18,1989 now U.S. Pat. No. 5,028,151 which is a continuation of applicationSer. No. 07/226,143, filed Jul. 29, 1988 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a bearing assembly for use in environs inwhich particular attention must be given to cleanliness and/or whereresistance to oxidation is paramount, such as in the food or chemicalindustry. More specifically, this invention relates to a bearingassembly having a cast iron housing coated in part with a low friction,chemically resistant polymer coating.

In the food, chemical and environmental industries there is a great needfor a bearing assembly which resists rust, and will not chip, flake ordeteriorate in severe wet operating environments or under high pressurewashdowns. It is also important, in such environments, that the housingnot be subject to corrosion from chemicals normally encountered duringuse. In the past, cast iron housings of such bearing assemblies havebeen nickel plated to render the housing resistant to the chemical andenvironmental demands. In one example, where a ball bearing insert is toswivel into a spherical bore of a ball bearing housing, the housing boredimensions are controlled to give a specified swivel torque. Thisprocedure is used for a standard line of ball bearings.

When nickel plating is applied to such a ball bearing housing, thespherical bore must be machined oversize to allow for the platingbuildup, and requires an additional set up over standard machiningoperations. Furthermore, due to variations in plating thickness, ballbearing inserts to be used with the plated housings must be graded bysize and a trial and error assembly procedure has to be employed toachieve a desired swivel torque with the assembly.

Various and sundry products have heretofore been coated withfluorocarbon polymers such as a polytetrafluorotheylene, or productsthemselves have been made of such products, particularly to takeadvantage of low friction characteristics of the polymer. It is alsobelieved, though not known, that bearing inserts may have been producedbefore and coated with fluorocarbon polymers.

Bearing assemblies according to the present invention representimprovement over the prior art. Particularly, bearing assembliesaccording to the present invention are fully protected from theenvironment, are more uniform, and operate at desired assembly torquelevels. Moreover, with assemblies according to the present invention,trial and error matching of housings and inserts is no longer necessary.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved bearingassembly which is coated with a fluorocarbon polymer which avoidsproblems previously encountered with nickel plated cast iron bearingassembly housings.

It is another object of the present invention to provide a fluorocarbonpolymer coated cast iron bearing assembly which is resistant tocorrosive effects of chemicals and the like.

It is another object of the present invention to provide a food bearingassembly which can be utilized at a predictable swivel torque level.

The above objects are realized by providing a thin coating of afluorocarbon polymer on the outer surfaces of a cast iron housing of abearing assembly which is to be exposed to chemical action in foodprocessing or in chemical industries, and the like. The polymer coatingis preferably applied by a process which permits the thickness of thecoating to be closely controlled, and with which standard ball bearinghousings and inserts can be employed without special grading todifferent sizes and trial and error matching.

More particularly, preferably a first fluorocarbon polymer is applied tothe entire surfaces of the housing, and a second fluorocarbon polymer isapplied to the outer surface, while a dummy bearing insert is placed inthe bore opening within the housing to prevent deposition of the secondpolymer therein. An actual bearing insert received within the boreopening will then self seat therein and will exhibit a generally uniformswivel torque thereabout.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in conjunction with the attacheddrawings in which:

FIG. 1 is a perspective view partially in section of a bearing assembly;

FIG. 2 is a front view of the bearing assembly with the bearing insertin the insertion position;

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2 with thebearing insert in the insertion position; and

FIG. 4 is a view similar to FIG. 3, but showing displacement of thebearing insert in section to illustrate the bearing support for theshaft.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIGS. 1, 2 and 3, preferred embodiments of the presentinvention will be described. Bearing assembly generally 10 includes ahousing 12 which includes a base 14 having means thereon (not shown) forattachment of the assembly to a supporting surface. Housing 12 furtherincludes a spherical bore 16 therethrough and with curved inner surfaces18 which, in effect, are concave surfaces with respect to the outerdimensions of bore 16. A bearing insert generally 20 is provided andincludes a ball 22 and ball bearings, roller bearings or the like 26.Ball 22 of insert 20 is receivable within bore 16 where the peripheral,generally spherical surfaces 28 of same engage concave surfaces 18. Ashaft 24 secured to and extending outwardly from the ball 22 may besupported by the bearings 26. The application of a given swivel torqueto the shaft 24 moves the insert 20 a predetermined amount about thebore 16.

Housing 12 is manufactured of cast iron which is chemically cleanedbefore the exterior surfaces of same are provided with a protectivecoating of a fluorocarbon polymer. The protective coating is resistantto chemical attack, to corrosion, is unaffected by normal operatingtemperatures and has low friction characteristics. Before the coating isapplied to the housing 12, however, an insert is placed within bore 16to mask the curved inner surface 18. A "dummy" duplicate of the ball 22is preferred and is inserted into bore 16, after which the entire unitis shot blasted which roughens the surface of the unit. The insertion ofthe dummy into the bore 16 ensures that curved surface 18 of bore 16 isunaffected by the shot blasting and therefore remain smooth. The dummyinsert is thereafter removed from the bore 16 before the polymer coatingis applied.

The preferred polymer coating for housing 12 includes a first or primercoating 30 and a top coating 32. Primer polymer coating 30 for thehousing 12 is preferably a fluorinated ethylene-propylene polymer, whichaffords a heavy-duty, non-stick surface for receipt of ball 22 of insert20. Whereas the prior art assemblies required trial and error matchingof bearing inserts and housings, such is not required for the bearingassemblies according to the present invention. Instead, the pliantnature of primer coating 30 permits receipt of virtually all of a givensize ball even though normal tolerances may exist. At the same time,there is a generally same swivel torque experienced with all of theassemblies of the present invention. The primer coating 30 is not onlychemically inert and unaffected by harsh environs, but is also generallyreceptive of ball 22 of a bearing insert in a much improved fashion thanthe prior art structures. The fluorinated ethylene-propylene polymerprimer coat is generally produced by copolymerization oftetrafluoroethylene and hexafluoropropylene and predominantly is made upof linear chains of ##STR1## The fluorinated ethylene-propylene polymermay be provided in any suitable form for application to the bearinghousing of the present invention. In a most preferred application, asnoted above, a spray coat is applied and the polymer further includes aphenolic binder and exhibits thermoset characteristics. Suitablecommercial polymers include TEFLON 959-200 series resin manufactured byDuPont Company, Wilimington, Del. and FEP resins of LNP EngineeringPlastics, Malvern, Pa.

Curved surfaces 18 within bore 16 of housing 12, as noted above havehistorically been nickel plated, and so plated have encountered therestrictions and problems noted above. According to the presentinvention, the entire housing 12 (including the bore 16) is firstprovided with a primer polymer coating 30 having a thickness of fromabout 0.3 mil to about 0.5 mil. The primer coating should be heatresistant to 425° F. (218° C.) on a continuous bases, and up to 450° F.(232° C.) on an intermittent basis, without any appreciable loss ofphysical properties. The abrasion resistance as tested with a BellAbrasion Tester should be between 30 to 50 gms/mil. An abrasionresistance sliding arm test with a 500 gm load at 1000 cycles (#400Emery Paper with 5.5 sq. in. surface) produced a 9.3 mg. weight loss.

After the primer coating 30 is applied to the housing 12, the dummyduplicate of the insert 20 is reinserted into the bore 16. A top coating32 is then applied to the housing 12, the top coating 32 effectivelycovering the entire surface of the housing except curved inner surface18.

A preferred polymer for the top coating 32 of the surface of housing 12is a perfluoralkoxy polymer which is a thermoplastic polymer.Perfluoroalkoxy polymers contain repeat units of ##STR2## Again, as withthe fluorinated ethylene-propylene polymer, various ingredients may beadded to the perfluoralkoxy polymer to render same suitable for aparticular coating technique. A preferred polymer that is used in spraycoating is TEFLON P 532-700 manufactured by DuPont Company. Top coating32 is preferably applied by a spray coating process to achieve a uniformcoating thickness of up to 4.0 mils and preferably between about 1 andabout 3 mils. The top coating should be heat resistant to 500° F. (260°C.) on a continuous basis and up to 550° F. (288° C.) on an intermittentbasis. The top coating kinetic coefficient of friction against polishedsteel is 0.1. The water absorption of the top coating is limited to amaximum of 0.03%.

The primer coating 30 should have a combination of low frictioncharacteristics and surface elastic characteristics which allows thebearing insert 20 to seat itself in the housing's spherical bore 16without destroying the corrosion resistant coating. The polymer coatinghas non-stick surface characteristics that nickel plating does not havewhich also is very important in the food and chemical industry forwashdown and contamination avoidance, and offers greater resistance tocorrosive and chemical attack.

While particular preferred polymers have been described, it should benoted that any form of fluorocarbon polymer which may be suitablyapplied to cast iron and which has non-sticking, chemically resistantcharacteristics, can be employed to coat the exterior and interiorsurfaces of the bearing housing for the purposes of this invention.

Furthermore, it should be noted that the form of the housing disclosedherein is given only by example, and is not deemed to be limiting on theinvention. Obviously, any type of bearing housing that is going to beexposed to the corrosive effect of food and chemical attack, willbenefit from the polymer coating considered herein. It is obvious thatmany changes may be made herein without deviating from the scope of theclaims appended hereto.

What is claimed is:
 1. A method for making a bearing assembly suitablefor use in a wet or harsh chemical environment and a housing for usetherewith comprising:a) providing a cast iron housing defining aspherical bore therethrough; b) chemically cleaning said housing; c)placing an insert within said spherical bore, said insert conformingexactly to said spherical bore; d) roughening said housing with saidinsert disposed within said spherical bore to mask said spherical boreduring said roughening; e) removing said insert from said sphericalbore; f) applying a spray-coated polymer primer coating to said housingand said spherical bore; g) replacing said insert within said sphericalbore; h) applying a spray-coated polymer top coating to said housingwith said insert disposed within said spherical bore to mask saidspherical bore during application of polymer top coating; and i)removing said insert from said spherical bore.
 2. A method as in claim 1wherein said primer coating has a thickness between 0.3 and 0.5 mil. 3.A method as in claim 1, further comprising inserting a bearingsub-assembly defining a hole therethrough into said spherical bore afterthe second removal of said insert from said spherical bore.
 4. A methodas in claim 3, further comprising inserting a shaft into said bearingsub-assembly hole after inserting said bearing sub-assembly into saidspherical bore.
 5. A method for making a bearing assembly suitable foruse in a wet or harsh environment comprising the steps of:a) providing acast iron housing defining a spherical bore therethrough; b) chemicallycleaning said housing; c) placing an insert within said spherical bore,said insert conforming to said spherical bore; d) roughening saidhousing with said insert disposed within said spherical bore to masksaid spherical bore during said roughening; e) removing said insert fromsaid spherical bore; f) applying a polymer primer coating to fully coverouter surfaces of said housing and surfaces defining said sphericalbore, said polymer coating having a low porosity, exhibiting lowfriction characteristics and exhibiting thermoset characteristics, saidcoating being applied in a thickness in a range of from about 0.3 toabout 0.5 mil; g) replacing said insert within said spherical bore; h)applying a polymer top coating to said outer surfaces of said housingwhile said insert is disposed within said spherical bore to mask saidsurfaces of said spherical bore, said top coating having a low porosity,low friction characteristics and exhibiting thermoplasticcharacteristics, said top coating being applied in a thickness of fromabout 1.0 to about 5.0 mils; and i) removing said insert from saidspherical bore.